Question

In a waveguide, which condition always holds good?

• A. Phase velocity = C
• B. Phase velocity greater than C
• C. Phase velocity less than C
• D. Group velocity = C

Hint:

In waveguides, phase velocity is always greater than the speed of light.

Answer 1

The Correct Option is B

In a waveguide, the phase velocity \( v_p \) is always greater than the speed of light \( C \). This is due to the waveguide boundary conditions altering wave propagation. The phase velocity is given by:
\[ v_p = \frac{C}{\cos \theta} \] which is always greater than \( C \). However, this does not violate relativity since the group velocity \( v_g \) remains below \( C \).